Added option to force Appirater always to open App Store (instead of SKStoreProductViewController in iOS 6)

Sometime you don't want use SKStoreProductViewController, e.g., due autorotation issues.
Merge pull request #108 from amjaliks/features/appstore

Added option to force Appirater always to open App Store (instead of SKS...
Merge branch 'master' of git://github.com/arashpayan/appirater